Connected: An Internet Encyclopedia
RFC 1157 - 4.1. Elements of Procedure

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### 4.1. Elements of Procedure

This section describes the actions of a protocol entity implementing the SNMP. Note, however, that it is not intended to constrain the internal architecture of any conformant implementation.

In the text that follows, the term transport address is used. In the case of the UDP, a transport address consists of an IP address along with a UDP port. Other transport services may be used to support the SNMP. In these cases, the definition of a transport address should be made accordingly.

The top-level actions of a protocol entity which generates a message are as follows:

1. It first constructs the appropriate PDU, e.g., the GetRequest-PDU, as an ASN.1 object.

2. It then passes this ASN.1 object along with a community name its source transport address and the destination transport address, to the service which implements the desired authentication scheme. This authentication service returns another ASN.1 object.

3. The protocol entity then constructs an ASN.1 Message object, using the community name and the resulting ASN.1 object.

4. This new ASN.1 object is then serialized, using the basic encoding rules of ASN.1, and then sent using a transport service to the peer protocol entity.

Similarly, the top-level actions of a protocol entity which receives a message are as follows:

1. It performs a rudimentary parse of the incoming datagram to build an ASN.1 object corresponding to an ASN.1 Message object. If the parse fails, it discards the datagram and performs no further actions.

2. It then verifies the version number of the SNMP message. If there is a mismatch, it discards the datagram and performs no further actions.

3. The protocol entity then passes the community name and user data found in the ASN.1 Message object, along with the datagram's source and destination transport addresses to the service which implements the desired authentication scheme. This entity returns another ASN.1 object, or signals an authentication failure. In the latter case, the protocol entity notes this failure, (possibly) generates a trap, and discards the datagram and performs no further actions.

4. The protocol entity then performs a rudimentary parse on the ASN.1 object returned from the authentication service to build an ASN.1 object corresponding to an ASN.1 PDUs object. If the parse fails, it discards the datagram and performs no further actions. Otherwise, using the named SNMP community, the appropriate profile is selected, and the PDU is processed accordingly. If, as a result of this processing, a message is returned then the source transport address that the response message is sent from shall be identical to the destination transport address that the original request message was sent to.

4.1.1. Common Constructs
4.1.2. The GetRequest-PDU
4.1.3. The GetNextRequest-PDU

4.1.3.1. Example of Table Traversal

4.1.4. The GetResponse-PDU
4.1.5. The SetRequest-PDU
4.1.6. The Trap-PDU

4.1.6.1. The coldStart Trap
4.1.6.2. The warmStart Trap
4.1.6.3. The linkDown Trap
4.1.6.4. The linkUp Trap
4.1.6.5. The authenticationFailure Trap
4.1.6.6. The egpNeighborLoss Trap
4.1.6.7. The enterpriseSpecific Trap

Next: 4.1.1. Common Constructs

Connected: An Internet Encyclopedia
RFC 1157 - 4.1. Elements of Procedure